Complete the function to determine the number of bits required to convert integer A to integer B (where A and B >= 0)
The upper limit for A and B is 216, int.MaxValue or similar.
For example, you can change 31 to 14 by flipping the 4th and 0th bit:
31 0 0 0 1 1 1 1 1
14 0 0 0 0 1 1 1 0
--- ---------------
bit 7 6 5 4 3 2 1 0
Thus 31 and 14 should return 2.